The use of heating glass panes of the type described for equipping vehicles for air, sea or land transport is known. Such glass is notably used for windshields of airplanes, boats, automobiles, and trains, for example. The glass comprises a network made up of fine metallic wires arranged in parallel between two collector strips or buses connected to a source of electrical current located outside of the glass. These conductors, stretched in a straight line or bent in segments with rectilinear directrices, are most frequently undulated or curled along the rectilinear directrices with a view of better distribution for the dissipation of heat, of a reduction in the magnitude of the phenomena of optical diffraction caused by the presence of the network, and of an increase in the length of wire for a given distance between collector strips.
The electrical voltage, the diameter of the wire, the length of the wire and the spacing of the wires are determined with a view to producing a unit power rating, expressed in watts per square decimeter, of approximately 2 w/dm.sup.2 to 70 w/dm.sup.2 depending upon the use of the glass. Thus, for example, when the glass is used as a heating rear window or cap window or heating windshield in automobiles or trains, the unit rating generally ranges from 3 to 10 w/dm.sup.2. In marine transport, such heating panes generally have a unit rating of from 10 to 20 w/dm.sup.2, approximately, while in aviation such unit rating may vary from 15 to 70 w/dm.sup.2, approximately.
Whenever the vehicle is not limited in terms of electrical power, the entire windshield may be heated to prevent frost and "steam"; thus, in particular, the heating guarantees the proper operation of the windshield wipers.
Generally, however, vehicles, and in particular small aircraft, helicopters and small boats, are limited in terms of electrical power, in which case only a portion of the glass pane is heated.
In accordance with the known art, the resistance wires are arranged along rectilinear directrices that are generally parallel and only the collector strips may possibly be curved. Furthermore the strips, in view of their width, are usually situated at the edges of the glass pane in order not to hamper vision.
Windshield wipers used with such heating glass usually have circular translation or rotation movements. As a result it is impossible for the heating wires to completely cover the contour of the surface that the wipers sweep unless an area that extends substantially beyond the swept area is heated. This, however, requires a considerable amount of electrical power. The result is that only a small zone that fits in places within the area swept by the windshield wiper gets heated. The area of visibility is consequently greatly reduced in case of rain. Further there exists the danger that the windshield wiper, provided that it does not remain stuck when starting up, may at least undergo rapid wear and tear and have its operation greatly disturbed in case of frost on the portion of the area swept by it that is not heated.
It is therefore an object of the invention to overcome the aforementioned drawbacks and to create a heating network having an optimal heating area made up of fine electrical resistance wires embedded in a thermoplastic layer where the area coincides with the area to be swept by wipers.